Fluoroscopic x-ray tube mounting for a tiltable x-ray table to prevent misalignment



Jan. 7, 1969 R. J. MUELLER FLUOROSCOPIC X-RAY TUBE MOUNTING FOR A TILTABLE X-RAY TABLE TO PREVENT MISALIGNMENT Filed Oct. 51, 1966 FIG. 2A

I' II INVENTOR. ROBERT J. MUELLER WaW ATTORNEY United States Pat ent FLUOROSCOPIC X-RAY TUBE MOUNTING FOR A TILTABLE X-RAY TABLE TO PREVENT MIS- ALIGNMENT Robert J. Mueller, Brookfield, Wis., assignor to General Electric Company, a corporation of New York Filed Oct. 31, 1966, Ser. No. 590,898

US. Cl. 25057 Int. Cl. H01j 5/48; Hlllj 37/22 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates generally to diagnostic X-ray tables, and in particular, to improvement of the fluoroscopic assembly thereof.

Fluoroscopic examinations are conducted with the patient bearing on the top of an X-ray table which may be in various positions between horizontal and vertical. The fluoroscopic X-ray tube and X-ray beam collimator are mounted inside the body of the table so that the beam may project through the table top and patient and form an image which may be visualized on a fluorescent screen that is parallel with the table top. The screen and X-ray tube are supported from a tower which is mounted on rollers within the table for allowing the tower to be shifted laterally and longitudinally of the table in such manner that the central ray of the X-ray beam maintains coincidence with the center of the screen.

The support for the fluorescentscreen is usually a part of a spot-film tunnel which stores a film cassette and includes a mechanism for projecting the cassette under the screen in order to make a radiograph after something is observed which the radiologist wants permanently recorded.

When the X-ray table is at or near horizontal, and if the collimator is properly adjusted, the defining rays of the X-ray beam cone will fall within the boundaries of the screen or film and the central ray will coincide with their centers. However, when the table is angulated to a vertical position, the tower deflects because the weights,

of the spot-film tunnel and the X-ray tube casing are acting on opposite sides of the place at which the tower is mounted. Under this condition, the longitudinal axis of the X-ray tube is no longer truly vertical nor is the central ray of the X-ray beam truly horizontal, in which case an edge of the X-ray image overlaps or shifts off of the edge of the film or screen. A small angular error in the X-ray tube axis causes significant image because the beam movement is amplified by the relatively great distance between the focal spot of the tube and the surfaces on which the beam impinges. Moreover, if the collimator is mounted separately from the X-ray tube, the collimator also tends to misalign and cut off a side of the beam cone, thus aggravating the misalignment of the tube.

The conventional approach to remedying this condition has been to make the spot-film tower more massive in order to obtain greater rigidity. However, this conflicts with an opposite objective which is to keep the mass of the spot-film tower and its afliliated components low so that little power is required to shift the tower manually or with a motor drive quickly to any desired position with respect to the table top.

The present invention solves the above outlined problem by taking the unconventional approach of making the X-ray tube supporting structure less rigid rather than more rigid. More, particularly, in accordance with the invention, the X-ray tube and collimator are joined and the X-ray tube casing is attached at its opposite ends to itscarriage by means of two relatively flexible members which form opposite and equal sides of a parallelogram. A side that is adjacent and connects the flexible members coincides with the longitudinal axis of the X-ray tube casing. When the table is horizontal, the X-ray tube casing is suspended straight down from the flexible members which are then loaded only in tension. The longitudinal axis of the X-ray tube forms a rectangle with the flexible members under this condition. When the table is tilted vertically, each flexible member deflects by the same amount under the cantilever loading imposed by the X- ray tube casing, but the members remain in parallelism and the axis of the X-ray tube casing also remains parallel with the table top since the axis is one side of a closed parallelogram. Thus, the X-ray beam remains horizontal. There is a small shift of the horizontal beam in a vertical direction in this case, but it is inconsequential and usually not perceptible because the distance amplification described above is not present when the X-ray tube does not turn ang-ularly.

Generally speaking, it is an object of this invention to improve fluoroscopic X-ray techniques.

Specific objects of the invention are to mount a fluoroscopic X-ray tube in such manner that its axis and a viewing device are maintained in parallelism when the X-ray table is angulated to positions other than horizontal and to achieve this end by simple, inexpensive and yet effective means.

Achievement of the foregoing and other more specific objects will appear from time-to-time throughout the course of the ensuing specification.

An illustrative embodiment of the invention will now be described in reference to the drawing in which:

FIGURE 1 is a perspective view of an X-ray table and the principal components of a fluoroscopic device which incorporates the invention;

FIGURE 2A is a front view of the X-ray table of FIGURE 1 with its top disposed in a horizontal position;

FIGURE 2B shows the X-ray table angulated to a vertical position and with the parallelogram mounted X-ray tube casing shifted vertically by an amount that is exaggerated in order to illustrate the invention; and,

FIGURE 3 shows the disposition of the X-ray tube casing when the X-ray table is angulated vertically and the X-ray tube casing is mounted in the manner of the prior art.

FIGURE 1 shows the outline of an X-ray table body that is provided with a patient supporting top 11. The body is mounted on a floorstand 12 in respect to which the body may be tilted to move the patient to various positions between horizontal and vertical. The mechanism for angulating the table and for translating it so its end clears the floor when angulating is omitted for clarity and because it forms no part of the instant invention.

The table is provided with a fluoroscope tower 13 which has a spot-film tunnel 14 that projects laterally over the table and is adapted for movement vertically on tower 13. The top and front part of the spotfilm tunnel is provided with an X-ray image sensitive means such as a fluorescent screen 15. In many cases, an amplifying X-ray-to-optical-image converter, not shown, is used instead of screen 15. Within the back part of tunnel 14, but not shown, is a film cassette storage area and mechanism for projecting the cassette under the fluoroscopic screen 15 to enable taking a radiograph of the image on the screen when desired. The features described thus far are conventional and well-known.

Projecting into table body 10 from the bottom of tower 13, which is primarily a support structure, is an X-ray tube carriage 16. The carriage is ordinarily supported on tracks, not shown, which permit the tower to be moved laterally and longitudinally of the table. An X-ray tube casing 17 is suspended from carriage 16. Attached to the X-ray tube casing is an X-ray beam collimator box 18 for defining the X-ray beam so that no more of the patient is irradiated than is necessary to form a full size image on fluorescent screen 15 or the cassette inside of tunnel 14. Collimator 18 may be similar to one described in US. Patent No. 3,206,604, issued to L. S. Burchell, on Sept. 14, 1965, and assigned to the assignee of the instant invention.

FIGURE 1 illustrates how the X-ray tube casing and the collimator 18, which is attached to it, are suspended from carriage 16 on a pair of flat relatively thin sheet metal plates 19. These plates are formed as channels having flanges 19 to facilitate their being attached at the top to carriage 16 and at the bottom to the X-ray tube casing 17, as can be seen more clearly in FIGURE 2A which omits the attaching screws. When the X-ray table is horizontal and tower 13 is vertical as it is in FIGURES 1 and 2A, the plates 19 form the ends of a rectangle that has one long side formed by carriage I6 and the other long side parallel with the longitudinal axis of X-ray tube casing 17. When the table is in this position, one may see in FIGURE 2A that the X-ray beam, which is defined by broken lines, projects from the focal spot in tube casing 17 through the collimator and impinges centrally on the film in cassette 20 if it has been projected forward by the spot-film device or on fluorescent screen 15. In practice, the collimator 18 is adjusted so that the limiting rays of the beam fall within the boundaries of the fluorescent screen 15 and the film area that is being exposed in cassette 20.

When the X-ray table is angulated from its horizontal position of FIGURE 2A to its vertical position as shown in FIGURE 2B, the spot-film tower tends to deflect or shift vertically due to its own weight and the X-ray tube casing 17 tends to shift vertically under the influence of gravity. Ordinarily, this would cause significant misalignment of the X-ray beam with the fluorescent screen 15 and cassette 20. However, in accordance with the present invention, the tube casing supporting plates 19 flex at the corner formed by the plates and their flanges 19' and assume a parallelogram configuration which, in turn, maintains the longitudinal axis of X-ray tube casing 17 in parallelism with the table top 11 for any position between horizontal and vertical. In practice, the parallelogram departs very little from a true rectangle, but sufiiciently to avoid the axis of tube casing 17 assuming an acute angle with respect to the plane of table top 11.

The minor shifting of casing 17 in the long direction of the parallelogram causes the projected X-ray image to shift just enough to correct for the deflection of the spotfilm tunnel including the screen and cassette. There is no motion amplification about a pivot point.

Conditions prevailing in FIGURE 2B may be compared with those in FIGURE 3, which shows an X-ray tube casing 17 purportedly rigidly mounted in a conventional manner. In this case, regardless of the stiflness of the design, the axis of tube casing 17 is inclined to rotate as shown and assume an acute angle with respect to the plane of table top 11 as a result of distance and motion amplification. One may see in FIGURE 3 that the upper defining ray of the X-ray image is projected beyond the edge of either the film cassette 20 or screen 15 thus producing an off-center and only partial picture. It has never been possible to build enough strength into the spot-film tower and the X-ray tube casing support to avoid this situation completely. Moreover, the condition has become more bothersome in recent years since a heavy image amplifier is often attached in place of the fluorescent screen 15.

One may see particularly well in FIGURE 2B that there is additional merit in mounting collimator 18 directly on tube casing 17. With this arrangement, the easing and collimator shift in parallel by the same amount so that the collimator does not contribute to cutting off any more of the beam. Contrast this with the condition in FIGURE 3 where the tube casing 17 and collimator 19 become misaligned as a result of the casing tilting and the collimator remaining stationary in which case more of the beam is cut ofi than would normally be the case if only the tube were tilted when the X-ray table is positioned vertically.

Although one method for mounting an X-ray tube casing on a support that assumes a parallelogram shape when the table is tilted vertically has been described, those versed in the art of mechanical design will derive from this design suggestions for parallelogram supports that use something other than the flexible plates. For instance, the tube support can be made to pendulate on pivot points instead of flexing at the corner of the flanges 19 and side plates 19. Therefore, it should be understood that the design shown is illustrative rather than limiting, for the invention may be variously embodied and is to be limited only by construing the claims which follow.

It is claimed:

1. X-ray apparatus comprising:

(a) an X-ray table including a table top,

(b) a spot-film tower that is translatable laterally and longitudinally with respect to the table,

(c) a spot-film tunnel supported on the tower and extending laterally across one face of the table top,

(d) an X-ray tube carriage extending from the tower laterally across the other face of the table top, said tunnel and carriage tending to shift cross-wise of the tower and in the same direction under the influence of gravity when the tower becomes more nearly horizontal as a result of the table being tilted toward vertical position,

(e) an X-ray tube casing and means for supporting the casing from the carriage in a direction away from the tunnel,

(f) the last-named supporting means comprising members that are attached respectively near opposite ends of the casing and to the carriage and are adapted to deflect to form opposite sides of a parallelogram when the longitudinal axis of the casing is other than substantially horizontal, the said longitudinal axis forming another side of a parallelogram that maintains substantial parallelism with the tunnel.

2. The invention set forth in claim 1 wherein:

(a) said members comprise metal plates that deflect under the weight of the tube casing.

3. X-ray apparatus comprising:

(a) a support structure,

(b) an X-ray image visualizing means and an X-ray tube casing having a longitudinal axis, said means and easing each being mounted on the structure spaced apart from each other, said structure being adapted for being angulated between vertical and horizontal positions in which case the visualizing means and tube casing tend to shift under the influence of gravity crosswise of the structure,

(0) a pair of members interposed between the support structure and the casing and attached respectively near opposite ends of the casing and to the support structure, the said members being adapted to deflect in the same direction when the longitudinal axis of the casing is tilted to other than horizontal position, whereby said members form a parallelogram in conjunction with each other and the longitudinal axis of the casing.

References Cited UNITED STATES PATENTS 5/1935 Pohl 250-58 5/1951 Mueller et a1. 25058 WILLIAM F. LINDQUIST, Primary Examiner.

US. Cl. X.R. 

